Virginia Best1, H. Steven Colburn1, Lucas S. Baltzell1
Department of Speech, Language and Hearing Sciences, Boston University, Boston, USA

While many studies have reported a loss of sensitivity to interaural time differences (ITDs) carried in the fine-structure of low-frequency signals for listeners with hearing impairment (HI), relatively few data are available on the perception of ITDs carried in the envelope of high-frequency signals ITDs in this population. The few studies that exist found stronger effects of hearing loss at high frequencies than at low frequencies, but small subject numbers and several confounding effects prevented strong conclusions from being drawn. In the present study, we revisited this question while addressing some of the issues identified in previous studies. First, we focused on “rustle” stimuli that contain strong envelope fluctuations at high frequencies and thus have the potential to provide salient envelope ITDs. Second, we carefully equated sensation level across listeners and tested two different levels per listener, to better characterize effects of level. Third, we included young listeners in the HI group to tease apart effects of hearing loss and age. ITD discrimination thresholds were measured for 15 HI listeners and 10 listeners with normal hearing (NH). The stimuli were octave-band-wide rustle stimuli centered at 500 Hz or 4 kHz, which were presented at 20 dB or 40 dB sensation level. Broadband rustle stimuli and 500-Hz pure-tone stimuli were also tested. Overall, hearing loss had a detrimental effect on ITD discrimination. For the majority of HI listeners, their ITD deficit relative to the NH group was equivalent at low and high frequencies. For a handful of HI listeners, the deficit was strongly frequency-dependent. The results provide new data to inform binaural models that incorporate effects of hearing impairment.

Acknowledgements: This work was supported by NIH-NIDCD award DC015760.